a) Field of the Invention
The invention relates to an arrangement for displaying images on a projection screen, which arrangement includes a laser, which emits a laser beam, and a deflecting means, which is provided for deflecting the laser beam, and an image-generating means which is connected to a controlling device for controlling the laser and the deflecting means.
b) Description of the Related Art
Image-generating means are increasingly used for light effects in show business for entertainment and information, not only within enclosed spaces, but also in the open. In addition, a laser television apparatus, in which lasers are also used to generate images, is being developed.
In these fields of application, in which the effective radiation of the lasers is within the visible region of the spectrum and in which several watts of medium power is required, the spatial region to which the laser has access is detrimental to the health of human beings. This is particularly true in the case of vertical projection, where persons may be located between the image-generating means and a projection screen. Persons are at risk if they happen to come into the immediate range accessible to the projecting laser. It is possible for this risk to be extremely high when the laser used for the projection is directed immediately at a person, owing to interference with the projector, e.g. when the deflecting means stalls.
Yet safety risks cannot be ruled out even in the case of back projections, during which the viewers are generally separated from the laser apparatus by means of a projection screen, even if the entire laser projection system were to be located in a closed housing. For example, a service technician is required to open the housing and to observe the image, in order to adjust it. In so doing, it is possible that parts of his body may fall within the range accessible to the laser.
For lasers used in shows in which the public may happen to enter into that area which is swept by the laser, standards for precautionary means are being prepared in a number of countries. In this regard, the proposed standards are, however, no more than simple contrivances, such as providing a key-operated switch for opening a housing, or an emergency switch. In addition, there are regulations to the effect that lasers shows are to be controlled such that no laser beam will unintentionally fall into the auditorium. The risks to which the public is exposed remain very high, even if these regulations are adhered to, such that it is desirable to provide for increased safety in respect of the arrangement as set out above.
Safety devices are, however, known from other technical fields. Thus, U.S. Pat. No. 5 221 977 proposes, by using spectrum-selective means, to screen off only certain wave lengths and, instead, use holographic elements. The disadvantage in this regard is that information is filtered out at these wavelengths which, in an image-generating means of the type mentioned, is actually intended to reach the eye of the viewer.
Other safety devices include means for switching off the laser, or for reducing the light output power, when no defined reflection is noted in that region into which the laser is directed. Safety devices of this kind are described, for example in DE 33 40 427 A1 and in WO 94 28 972. In particular, the latter printed document describes a device in which a laser is designed to be switched on only when that part of the body, which is to be exposed to the laser for medical purposes, screens the laser from the other parts of the body. Thus, the laser is switched on only when, for example, a finger to be exposed covers an outlet opening for the laser burst.
It is not possible to use safety systems of this kind in arrangements for image generation according to the state of the art as set out above, since here the laser beams must remain visible to the spectators. As stated above, experts on standardization committees make no mention of any means whereby it would be possible to prevent persons from accidentally entering into the hazardous area swept by the laser.